U.S. patent application number 12/061180 was filed with the patent office on 2008-12-25 for hydraulic tensioner.
This patent application is currently assigned to TSUBAKIMOTO CHAIN CO.. Invention is credited to Yuji Kurematsu.
Application Number | 20080318717 12/061180 |
Document ID | / |
Family ID | 39409941 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080318717 |
Kind Code |
A1 |
Kurematsu; Yuji |
December 25, 2008 |
HYDRAULIC TENSIONER
Abstract
A hydraulic tensioner comprises a plunger, and a
plunger-accommodating hole in a tensioner housing, together forming
a high pressure oil chamber. A plunger-biasing spring is provided
in the high pressure oil chamber between the plunger and the bottom
of the plunger-accommodating hole. An oil storage chamber is formed
inside the plunger, and a check valve unit is press-fit in the rear
end of the plunger to allow flow from the oil storage chamber to
the high pressure oil chamber while blocking reverse flow of
oil.
Inventors: |
Kurematsu; Yuji; (Osaka,
JP) |
Correspondence
Address: |
HOWSON AND HOWSON
SUITE 210, 501 OFFICE CENTER DRIVE
FT WASHINGTON
PA
19034
US
|
Assignee: |
TSUBAKIMOTO CHAIN CO.
Osaka
JP
|
Family ID: |
39409941 |
Appl. No.: |
12/061180 |
Filed: |
April 2, 2008 |
Current U.S.
Class: |
474/110 |
Current CPC
Class: |
F16H 2007/0853 20130101;
F16H 7/0848 20130101; F16H 2007/0859 20130101; F16H 2007/0812
20130101; F16H 2007/0806 20130101 |
Class at
Publication: |
474/110 |
International
Class: |
F16H 7/08 20060101
F16H007/08; F16H 7/22 20060101 F16H007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2007 |
JP |
2007-166839 |
Claims
1. A hydraulic tensioner comprising: a housing having a
plunger-accommodating hole; a plunger slidable in the
plunger-accommodating hole and protruding therefrom in a protruding
direction, for applying tension to an endless, flexible, traveling,
timing transmission chain, said plunger having a hollow bore
extending from a rear end of the plunger to an internal location
adjacent an opposite end of the plunger, and forming an internal
oil storage space within the plunger; a plunger-biasing spring
accommodated in a high pressure oil chamber formed between said
plunger-accommodating hole and a rear end of said plunger, said
spring biasing the plunger in said protruding direction; and a
check valve unit, press-fit in the rear end of said plunger and
closing said internal oil storage space, the check valve unit being
arranged to allow flow of oil from said internal oil storage space
to said high pressure oil chamber while blocking reverse flow of
oil from the high pressure oil chamber to the oil storage
space.
2. A hydraulic tensioner according to claim 1, having an oil supply
hole connecting the internal oil storage chamber to the exterior of
the plunger, for supplying oil to said internal oil storage
chamber, in which the housing has an oil supply bore providing a
path for flow oil form the exterior of the housing to the interior
of the plunger-accommodating hole; in which the plunger has an
outer peripheral surface and a recess formed in said outer
peripheral surface; in which said oil supply hole in the plunger
has an opening within said recess.
3. A hydraulic tensioner according to claim 2, in which the length
of the recess, in the direction of protrusion of the plunger, is
sufficient that the oil supply bore is in register with the recess,
to allow flow of oil from the oil supply bore to the oil supply
hole throughout the stroke of the plunger.
4. A hydraulic tensioner according to claim 3, in which the length
of the recess, in the direction of protrusion of the plunger, is
equal to the maximum stroke of said plunger.
5. A hydraulic tensioner according to claim 1, having an oil supply
hole connecting the internal oil storage chamber to the exterior of
the plunger, for supplying oil to said internal oil storage
chamber, said oil supply hole being located on a ridge line of the
plunger.
6. A hydraulic tensioner according to claim 5, in which the housing
has an oil supply bore providing a path for flow oil form the
exterior of the housing to the interior of the
plunger-accommodating hole; in which the plunger has an outer
peripheral surface and a recess formed in said outer peripheral
surface; in which said oil supply hole in the plunger has an
opening within said recess.
7. A hydraulic tensioner according to claim 6, in which the length
of the recess, in the direction of protrusion of the plunger, is
sufficient that the oil supply bore is in register with the recess,
to allow flow of oil from the oil supply bore to the oil supply
hole throughout the stroke of the plunger.
8. A hydraulic tensioner according to claim 7, in which the length
of the recess, in the direction of protrusion of the plunger, is
equal to the maximum stroke of said plunger.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority on the basis of Japanese
patent application 2007-166839, filed Jun. 25, 2007. The disclosure
of Japanese application 2007-166839 is hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to hydraulic tensioners for
maintaining proper tension in a timing chain such as a roller
chain, a silent chain, or the like, in a vehicle engine. The
invention relates more specifically to a hydraulic tensioner in
which an oil storage chamber is formed within the plunger of the
tensioner.
BACKGROUND OF THE INVENTION
[0003] Hydraulic tensioners comprising housings with protruding
plungers have been used in vehicle engines for maintaining tension
in timing chains that transmit rotation from an engine crankshaft
to one or more valve-operating camshafts. The plunger usually
engages a movable guide having a shoe on which a portion of the
chain traveling away from a crankshaft sprocket slides. The plunger
is urged by a plunger-biasing spring in the protruding direction,
and the plunger and a portion of a plunger-receiving hole in the
tensioner housing together form a high pressure oil chamber for
containing oil that leaks through a restricted path, usually
between the plunger and the wall of the plunger-receiving hole.
Leakage of the oil has a damping effect on retracting movement of
the plunger, thereby suppressing vibrations while maintaining
proper tension.
[0004] Tensioners are mounted in various orientations on an engine
block, depending on available space and on the presence of other
engine parts. These mounting orientations include orientations in
which the plunger protrudes upward, or obliquely upward.
[0005] U.S. Pat. No. 6,045,471 describes a tensioner having an
upwardly protruding plunger. The tensioner has a hydraulic buffer
mechanism comprising a hollow, tubular, plunger sleeve formed with
a plunger insert bore extending axially through the sleeve. A
plunger fits slidably in the plunger insert bore, with its ends
projecting axially from the ends of the sleeve. The sleeve is
slidable in a plunger sleeve-receiving bore of a housing having an
open front end and a closed bottom end. The plunger-receiving bore
is formed as a continuation of the rear of the plunger sleeve, and
the rear portion of the plunger, projecting from the rear end of
the sleeve, is slidable in the plunger-receiving bore. A high
pressure oil chamber is formed between the bottom of the
plunger-receiving bore and the rear end of the plunger. A check
valve incorporated into the rear end of the plunger provides an oil
path for flow or oil into the high pressure chamber from an oil
supply reservoir inside the plunger. Oil is supplied to the oil
supply reservoir from a source external to the plunger housing
through an oil supply passage open at a rear portion of the plunger
sleeve-accommodating hole in the plunger housing, and an oil supply
hole provided on the outer circumferential surface of the
plunger.
[0006] An anti-retrograde mechanism is provided between the plunger
housing and the plunger sleeve to allow only forward displacement
of the sleeve with respect to the plunger housing. A plunger
spring, provided on the circumference of a portion of the plunger
projecting from the front end of the plunger sleeve, urges the
plunger in the protruding direction, and a sleeve spring provided
between the plunger housing and the plunger sleeve, and having a
smaller spring constant than the plunger spring, urges the plunger
sleeve forward. When a shock load acts on the front end of the
plunger, leakage of oil from the high pressure chamber through a
restricted clearance buffers the shock load. The restricted
clearance is proved by the sliding engagement between the inner
peripheral surface of the plunger-receiving bore and the outer
peripheral surface of the plunger.
[0007] The above-described hydraulic shock-absorbing tensioner has
a greater number of parts than the usual conventional tensioner and
a more complicated structure, since it includes a plunger sleeve
and a sleeve spring fitted between the plunger housing and the
plunger. The overall length of the plunger is necessarily greater
than the length of a plunger in the usual hydraulic tensioner.
Moreover, even though the plunger is longer than a conventional
plunger, the internal space available for storage of oil within the
plunger is limited, and is inadequate under some conditions of
operation where the demand for oil in the high pressure oil chamber
is high.
[0008] In the above-described hydraulic shock-absorbing tensioner,
the overlap of the mutually sliding surfaces of the plunger housing
and the plunger is short, and consequently the leakage of oil
through the restricted clearance between these mutually sliding
surfaces can become excessive. When the engine is not operated over
an extended period of time, oil drainage from the oil reservoir and
the high pressure chamber occurs as a result of leakage. Then, when
the engine is re-started, the hydraulic damping force exerted as a
result of oil leakage cannot be realized until oil is restored in
the oil reservoir and in the high pressure oil chamber. As a
result, troublesome backlash of the engine timing chain occurs on
engine start-up, abnormal sounds are generated, and unexpected
damage can occur. Furthermore, when the plunger of the tensioner
advances as a result of elongation of the timing chain, the
backlash on engine start-up is exaggerated. Similar exaggeration of
backlash in the engine timing drive can occur when the tensioner is
mounted so that the plunger protrudes upward at a small angle
relative to the horizontal.
[0009] Accordingly, an object of the invention is to overcome the
above-mentioned problems of the prior art, and to achieve one or
more of the following advantages, namely: providing a hydraulic
tensioner that has an sufficient oil reservoir located within its
plunger, ensuring an adequate supply of oil to its high pressure
oil chamber upon engine start-up even when the engine has not been
operated for a long interval of time; rapidly exhibiting hydraulic
damping upon engine start-up; preventing backlash and abnormal
sounds; and avoiding a large number of parts.
SUMMARY OF THE INVENTION
[0010] The hydraulic tensioner according to the invention comprises
a housing having a plunger-accommodating hole and a plunger
slidable in the plunger-accommodating hole and protruding therefrom
in a protruding direction. The plunger applies tension to an
endless, flexible, traveling, timing transmission chain. The
plunger has a hollow bore extending from a rear end of the plunger
to an internal location adjacent an opposite end of the plunger.
The hollow bore forms an internal oil storage space within the
plunger. A plunger-biasing spring, which urges the plunger in the
protruding direction, is accommodated in a high pressure oil
chamber formed between the plunger-accommodating hole and the rear
end of the plunger. A check valve unit, press-fit in the rear end
of the plunger, and closing its internal oil storage space, allows
flow of oil from the internal oil storage space to the high
pressure oil chamber while blocking reverse flow of oil from the
high pressure oil chamber to the oil storage space.
[0011] In a preferred embodiment of the invention, an oil supply
hole connects the internal oil storage chamber to the exterior of
the plunger in order to supply oil to the internal oil storage
chamber, and the housing has an oil supply bore providing a path
for flow of oil from the exterior of the housing to the interior of
the plunger-accommodating hole. The plunger has a recess formed in
its outer peripheral surface, and the oil supply hole in the
plunger has an opening within the recess. The oil supply hole is
preferably located on a ridge line of the plunger, the ridge line
being defined as the locus of the highest points of cross-sections
of the plunger taken on planes to which the direction of protrusion
of the plunger is perpendicular.
[0012] The length of the recess, in the direction of protrusion of
the plunger, should be sufficient that the oil supply bore is in
register with the recess throughout the stroke of the plunger, in
order to allow flow of oil from the oil supply bore to the oil
supply hole. The length of the recess is preferably equal to the
maximum stroke of the plunger.
[0013] The bore within the plunger extends nearly the entire length
of the plunger and can have a large diameter corresponding to the
diameter of the plunger-receiving hole less twice the thickness of
the wall of the plunger. As a result, the volume of the oil storage
chamber formed by the bore in the plunger can be made sufficiently
large to ensure an adequate supply of oil to the high pressure
chamber of the tensioner. Thus, when the plunger is pushed into the
plunge-accommodating hole, the supply of oil in the high pressure
chamber is always sufficient to damp the movement of the plunger.
Furthermore, when the plunger protrudes rapidly from the
plunger-accommodating hole, causing the oil pressure in the high
pressure chamber to drop, the oil in the high pressure oil chamber
is replenished rapidly so that hydraulic damping can take place
instantaneously when the plunger is again pushed into the
plunger-accommodating hole. As a result, backlash of the timing
chain is suppressed on engine start-up, and the generation of
abnormal sounds is prevented.
[0014] Positioning the oil supply hole in the plunger on the ridge
line of said plunger allows optimum utilization of the available
oil storage space in the oil storage chamber inside the
plunger.
[0015] The recess in the surface of the plunger maintains fluid
communication between the oil supply bore in the tensioner housing
and the oil supply hole in the plunger throughout the stroke of the
plunger. Thus a reliable supply of oil is provided, through the
housing, to the oil storage chamber inside the plunger.
Additionally, the number of parts required in the tensioner is
small compared to the number of parts in a tensioner utilizing a
plunger sleeve, and the tensioner is comparatively easy to
manufacture because difficult machining of the inside wall of the
plunger-accommodating hole in the housing is unnecessary. When the
length of the recess is sufficient that the oil supply bore is
always in register with the recess throughout the stroke of the
plunger, oil is always allowed to flow from the oil supply bore to
the oil supply hole, ensuring an adequate supply of oil in the oil
storage chamber inside the plunger. Furthermore, when the length of
the recess is made is equal to the maximum stroke of the plunger,
the overall length of the tensioner housing can be kept at a
minimum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic elevational view of an engine timing
transmission using a hydraulic tensioner in accordance with the
invention;
[0017] FIG. 2 is a perspective view of the tensioner, as viewed
from the rear;
[0018] FIG. 3 is a perspective view of the tensioner as viewed from
the front;
[0019] FIG. 4 is a perspective view of the plunger of the
tensioner;
[0020] FIG. 5 is a longitudinal cross-sectional view of the
plunger, including an enlargement of the check valve of the plunger
as an auxiliary view;
[0021] FIG. 6 is a schematic elevational view showing the hydraulic
tensioner attached to an engine, and illustrating the path of oil
flow into the oil reservoir in interior of plunger;
[0022] FIG. 7 is a cross-sectional view of the assembly shown in
FIG. 6;
[0023] FIG. 8 is a cross-sectional view of the tensioner, showing
oil stored in the oil reservoir inside the plunger, including an
enlargement of a part of the plunger-biasing spring and the check
valve as an auxiliary view;
[0024] FIG. 9 is a cross-sectional view of the tensioner, showing
the communication path for entry of oil into the reservoir within
the plunger, when the plunger is in an initial retracted condition,
including an enlarged auxiliary view of the oil flow path;
[0025] FIG. 10 is a cross-sectional view of the tensioner, showing
the communication path for entry of oil into the reservoir within
the plunger, when the plunger is in a fully extended condition,
including an enlarged auxiliary view of the oil flow path;
[0026] FIG. 11 is a perspective view of a plunger used in a second
embodiment of the invention; and
[0027] FIG. 12 is a longitudinal cross-sectional view of the
plunger of FIG. 11, including an enlarged auxiliary view of the
check valve assembly in the plunger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The invention will be described in the context of a
ratchet-type hydraulic tensioner adapted for use with a pivoted
chain guide or lever to maintain tension in the timing chain of a
vehicle engine. However, the invention can be embodied in a
tensioner wither with or without a ratchet mechanism, and also in a
tensioner in which a chain guide is carried by a plunger.
[0029] The hydraulic tensioner of the invention is preferably
attached in a vehicle engine in such a way that its plunger
protrudes upward at an angle relative to the horizontal. However,
the tensioner can be disposed so that its plunger protrudes
horizontally or downward at an angle relative to the
horizontal.
[0030] As shown in FIG. 1, a hydraulic tensioner 100, is attached
to an engine body EB on the slack side of a timing chain C, which
is extends from a crankshaft sprocket S1 to a camshaft sprocket S2.
Arrows indicate the direction of rotation of the sprockets. A
plunger 120 of the hydraulic tensioner 100 protrudes from the front
of a tensioner housing 110, and engages the back of a pivoted lever
L1 which is pivoted on the engine. The plunger engages the back of
the lever at a location remote from the lever's pivot axis. The
lever, in turn, is in sliding engagement with the chain C and
applies tension to the slack side of the chain. A fixed guide L2 is
in sliding engagement with the tension side of the chain.
[0031] As shown in FIGS. 2 and 3, the tensioner housing 110 is
attachable to an engine by an attachment plate 111 at the rear of
the housing. As seen in FIG. 3, the plunger 120 protrudes from a
plunger-accommodating hole 112 in the housing 110. The plunger is
urged in the protruding direction by a plunger-biasing spring 130,
shown in FIG. 7. the spring 130 is a coil spring in compression
within a high pressure oil chamber R formed in the plunger
accommodating hole 112 between the rear end of the plunger 120 and
the bottom of the plunger-accommodating hole.
[0032] As seen in FIG. 4, the plunger has an internal bore
extending axially from its rear end to a location adjacent its
protruding end. FIGS. 4 and 5 show a check valve unit 140, which is
press-fit into the bore of the plunger at the rear end of the
plunger, closing off the rear opening of the bore and forming an
internal oil storage chamber P within the plunger. The check valve
permits flow of oil outward from the storage chamber P into the
high pressure oil chamber R, but blocks reverse flow of oil from
the high pressure oil chamber R into the oil storage chamber P. A
ratchet mechanism 150, comprising a pivoted pawl 151 and a
pawl-biasing spring 152, cooperates with a rack 121 formed on the
outer circumferential surface of the plunger 120 to allow the
plunger to proceed gradually in the protruding direction as chain
elongation occurs. The ratchet mechanism, however, permits only a
limited degree of retracting movement of the plunger when a force
is applied to the plunger by the chain through the pivoted
lever.
[0033] As shown in FIGS. 4 and 5, the check valve unit 140 includes
a check ball 141 within a ball guide 142, which is the part that is
press-fit into the plunger. The ball fits loosely in the ball guide
and can move toward and away from a ball seat 143 which is
press-fit into the ball guide. The ball seat has an oil passage
143a communicating with the oil storage chamber P and an annular
seating surface 143b engageable by the check ball to close off the
passage 143a. The check ball is urged against the seating surface
143b by, a ball-biasing spring 144. Holes 142a in the bottom of the
ball guide are provided to allow oil to flow from the oil storage
chamber P, through the check valve unit, to the high pressure oil
chamber R.
[0034] As shown in FIGS. 2 and 3, the tensioner housing has a
concave dimple 113 formed in its exterior wall, leading to an oil
supply bore 114 that extends through the wall of the housing and
has an inner opening at the wall of the plunger-accommodating hole
112. FIGS. 6-10 illustrate the paths of oil flow from the engine
oil supply into the oil storage chamber P inside the plunger. As
shown in FIGS. 6 and 7, the tensioner housing is mounted in a part
of the engine body EB illustrated in broken lines. Oil, following
the path indicated by arrows, flows through a passage into an
annular groove surrounding the tensioner housing. The portion of
the housing wall in which the dimple 113 is located is surrounded
by the annular groove, and thus oil can flow through the groove to
the dimple, and from the dimple to the interior of the housing
through oil supply bore 114.
[0035] As shown in FIG. 8, the oil supply bore 114 is slanted
downward from the bottom portion of the concave dimple 113 Thus oil
flows downward through bore 114. The bore 114 is also slanted in
the direction of protrusion of the plunger 120 so that its opening
at the inner wall of the plunger-accommodating hole is located well
forward of the bottom of the plunger-accommodating hole. As shown
in FIG. 9, an oil supply hole 122 extends through the wall of the
plunger to the oil storage chamber P. With the opening of bore 114
located well forward of the bottom of the plunger-accommodating
hole, oil can fill most of the internal oil storage space within
the plunger.
[0036] The oil supply hole 122 is located on the ridge line of the
plunger, i.e., on the locus of the highest points of cross-sections
of the plunger taken on planes to which the direction of protrusion
of the plunger is perpendicular. Since the rack 121 of the plunger
must cooperate with the ratchet mechanism 150, the location of the
line of the plunger is necessarily in a predetermined relationship
with the rack.
[0037] A groove 123 in the outer periphery of the plunger provides
communication between the oil supply bore 114 in the housing 110
with the oil supply hole 122 in the plunger 120. The groove 123
provides oil communication throughout the entire stroke of the
plunger, without the need for a complicated tensioner structure in
which a plunger sleeve and a sleeve spring are fitted between the
housing and the plunger as in a conventional hydraulic
shock-absorbing tensioner.
[0038] The groove can be in the form of a simple flat shape milled
in the outer surface of the plunger and extending in the direction
of protrusion of the plunger. Because of the elongation of the
groove, continuous oil communication between the oil supply bore
114 in the housing and the oil supply hole 122 in the plunger is
maintained throughout the stroke of the plunger. Furthermore, as
shown in FIG. 5, the groove 123 has a length X, which is preferably
equal to the maximum stroke of the plunger 120, which is
illustrated in FIGS. 9 and 10. Thus, groove 123 accommodates the
maximum shift between the oil supply bore 114 in the housing and
the oil supply hole 122 in the plunger 120. FIGS. 9 and 10 show the
flow of oil from the oil supply bore 114 of the housing 114 to the
oil supply hole 122 of the plunger 120.
[0039] In the hydraulic tensioner 100, since the oil storage
chamber P occupies the entire inside area of the plunger 120, a
maximum oil storage space is provided. When the plunger 120 is
pushed into the plunger-accommodating hole 112, the amount of oil
present in the high pressure chamber R is always sufficient to
exhibit the necessary hydraulic damping. When the plunger 120
protrudes from the plunger-accommodating hole 112 oil from the oil
storage chamber P is rapidly supplied to the high pressure oil
chamber R, and consequently, there is no depletion of oil in the
high pressure oil chamber, and the hydraulic damping force can be
exhibited instantaneously whenever it is required. As result,
backlash of the timing chain C on engine start-up is suppressed and
generation of abnormal sounds can be prevented. These effects can
be realized not only when the tensioner is mounted so that the
plunger protrudes horizontally, but also when the tensioner is
mounted so that the plunger protrudes upward or downward.
[0040] Since the oil supply hole 122 is provided on a ridge line of
the plunger 120, the oil storage level in the oil storage chamber P
can be maintained at least to the level of the supply hole
position. Moreover, since the groove 123, which allows the oil
supply bore 114 in the housing 110 to communicate with the oil
supply hole 122 in the plunger 120 provides communication over a
margin X (FIG. 5) at least equal to the maximum stroke of the
plunger 120, the supply of oil to the oil storage chamber is
reliably maintained over the full stroke of the plunger.
Additionally, the number of parts required for the tensioner is
significantly lower than the number of parts in a conventional
hydraulic tensioner having a sleeve, and difficult machining of the
inner wall of plunger-accommodating hole in the housing can be
avoided. Thus the tensioner can be manufactured at a comparatively
low cost.
[0041] In the second embodiment of the invention as shown in FIGS.
11 and 12, components corresponding to components of the first
embodiment are designated by numbers that exceed by 100 the
reference numbers of the corresponding components in the first
embodiment.
[0042] In the hydraulic tensioner 200, an oil supply hole 222,
which provides for flow of oil into oil storage chamber P, is
disposed on a ridge line of the plunger 220, and as in the
above-described first embodiment, the oil storage level in chamber
P can be maintained at a level at least as high as the position of
the opening of hole 222 into the oil storage chamber P.
[0043] In the second embodiment, the groove that provides for
communication of oil from an oil supply bore (not shown) in the
housing is in the form of a cylindrical portion of the outer wall
of the plunger having a reduced diameter and a length X
corresponding to the maximum stroke of the plunger. The groove 223
can be formed easily by turning and has the same effect as the flat
milled surface in the plunger of the first embodiment. Here, as in
the first embodiment, the complicated structure of the conventional
hydraulic shock-absorbing tensioner is avoided, an adequate oil
storage space in the oil storage chamber P inside the plunger is
ensured, backlash of the timing chain C on engine start-up is
suppressed, and the generation of abnormal sounds can be
prevented.
[0044] Moreover, as in the first embodiment the tensioner of the
second embodiment can be mounted with the plunger protruding upward
or downward as well as horizontally, and the groove 223 maintains
communication between an oil supply bore in the tensioner housing
and the oil supply hole 222 in the plunger throughout the stroke of
the plunger, thus ensuring a reliable supply of oil to the oil
storage chamber P, and from the oil storage chamber P, through the
check valve unit 240, to a high pressure oil chamber formed by the
plunger and the plunger-accommodating hole in the tensioner
housing. As in the first embodiment, fewer parts than those of a
conventional shock-absorbing tensioner are required, and
manufacture is inexpensive, especially since difficult machining of
the inner wall of the plunger-accommodating hole of the tensioner
housing is unnecessary.
* * * * *